1. Technical Field
The present invention relates to a multilayered power inductor and a method for preparing the same.
2. Description of the Related Art
As a demand for small, thin, and multi-functional electronic products is increased, a chip component also requires large-current components. In order to improve high-current characteristics keeping pace with thinness and multi-functional characteristics, there is a need to reform a material and use advantages between respective materials based on complexation.
In the case of the multilayered chip component, as a material of a magnetic layer body, ferrite having a quaternary structure such as Ni—Zn—Cu—Fe is used. However, a saturation magnetization value of the material is lower than that of a metallic material, such that it is difficult to implement specifications required for high current characteristics. Therefore, a mixture of the ferrite material and a metal alloy has been mainly used.
Meanwhile, in order to increase efficiency of a power inductor, RDC characteristics are considered as a critical factor. In order to increase the RDC characteristics per a unit volume, there is a need to increase densification of an electrode after the multilayered power inductor is fired.
As illustrated in FIG. 1, the multilayered power inductor according to the related art is configured to include a magnetic layer body 10 made of a ferrite material having a quaternary structure such as Ni—Zn—Cu—Fe, an inner electrode 20, and an outer electrode 30. The inner electrode 20 and the outer electrode 30 mainly use silver (Ag) and the outer electrode 30 may further include a plating layer.
In order to increase the efficiency of the power inductor, it is important to implement high capacity and low RDC. In order to increase the capacity, there is a problem in that a pattern of the inner electrode 20 is designed to be widened maximally and a thickness of a cover A covering the body 10 and the inner electrode 20 and a cutting margin B should be secured. Further, in order to reduce the RDC, there is a limitation of a design in increasing a sectional area of the inner electrode. Therefore, it is important to improve the RDC characteristics by densifying the structure of the inner electrode in the same sectional area.
In the case of the multilayered power inductor according to the related art, the pattern of the inner electrode 20 is implemented in the body 10 by printing silver paste (Ag paste) using a screen printing method and is multilayered/cut and is then fired by a co-firing method, thereby performing the densification of the electrode. In this case, the silver paste of the inner electrode 20 is more quickly densified due to a rapid sintering behavior as compared with ceramic materials of the ceramic body 10 and after the silver paste is fired, a number of pores occurs in the inner electrode 20 due to the effect of residual carbon (carbon that is not completely removed during a calcination process). The densification of the inner electrode 20 is reduced and the RDC characteristics are degraded, due to these pores.
Therefore, the existing method uses ceramic powders equal to or smaller than a size of metal powders used in the inner electrode layer as a sintering inhibitor to limit a contact between the metal powders, thereby maximally delaying a shrinkage starting temperature of the inner electrode, but cannot expect a sufficient effect until now.
Further, at the time of co-firing the magnetic layer body 10 and the inner electrode 20, a delamination defect, such as a crack of the magnetic layer after the power inductor is fired, may frequently occur due to stress caused by the mismatching of the sintering behavior between the material of the inner electrode and the ceramic material of the magnetic layer body.